Tone count selection

ABSTRACT

In a device or system, a total tone count is determined or selected for modulating a data payload. Two or more code words are interleaved into the data payload, and the data payload is transmitted on a channel of the device or system.

RELATED APPLICATION

This application is a divisional of and claims priority to U.S. patentapplication Ser. No. 12/655,051, Attorney Docket No. IN1-0079US, filedon Dec. 22, 2009, and entitled “Tone Count Selection.”

BACKGROUND

Orthogonal frequency division multiplexing (OFDM) provides a useful wayto modulate data for transmission. OFDM may be considered a form ofdigital multi-carrier modulation. A large number of orthogonalsub-carriers are used to carry data. Data for transmission is thendivided into several parallel data streams for transmission. Each of thesub-carriers may in turn be modulated using binary phase-shift keying(BPSK), quadrature phase-shift keying (QPSK), quadrature amplitudemodulation (QAM), and so forth.

An OFDM system uses several carriers, or “tones,” for functionsincluding data, pilot, guard, and nulling. Data tones are used totransfer information between the transmitter and receiver via one of thechannels. Pilot tones are used to maintain the channels, and may provideinformation about time/frequency and channel tracking. Guard tones maybe inserted between symbols to during transmission to avoid inter-symbolinterference (ISI), such as might result from multi-path distortion.These guard tones also help the signal conform to a spectral mask. Thenulling of the direct component (DC) may be used to simplify directconversion receiver designs.

Selecting tone for use within a given OFDM system has provenproblematic, particularly when constraints such as reuse of existingOFDM components are included.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Thesame numbers are used throughout the drawings to reference like featuresand components.

FIG. 1 is an illustrative architecture of a tone selection module andOFDM modules using selected tones.

FIG. 2 is a flow chart of a process for selecting tones for use by anOFDM module.

FIG. 3 is an example script for selecting tones for use by an OFDMmodule.

FIG. 4 is a table of illustrative possible configurations for an OFDMsystem having an 80 MHz bandwidth.

FIG. 5 is a table of possible allocations for new modulation and codingtypes, based on a portion of the possible configurations of FIG. 4.

DETAILED DESCRIPTION Overview

OFDM is used for modulating communications both for wired and wirelessdevices. As described above, an OFDM system uses selected tones foroperation. These tones may be used for data, pilot, guard, DC, and otherfunctions.

Demands for higher capacity communications may result in modificationsto OFDM systems to increase capacity. It is beneficial for thesemodifications to make use of existing code and hardware where possible.For example, in a wireless OFDM system a deployedinterleaver/deinterleaver may be re-used in an OFDM system using largerbandwidth with minimal modification. This re-use minimizes developmentcosts and risk associated with new technologies.

Disclosed in this application is a system and techniques suitable forselecting tones for use by an OFDM system, such that existing OFDMcomponents may be leveraged and re-used with minimal or no changes. Inone example, a wireless communication system using OFDM with a 40 MHzchannel bandwidth may be extended to 80 MHz, increasing the datatransmission capacity of the system.

Illustrative Architecture

FIG. 1 is an illustrative architecture 100 of a tone selection moduleand OFDM modules using the selected tones. A device 102(1) is shown withan orthogonal frequency division multiplexing (OFDM) module 104(1) whichis coupled via a wired connection 106 to an OFDM module 104(2) in adevice 102(2). OFDM module 104 is configured to generate an OFDM signal.Also shown is a wireless device 102(3) having an OFDM module 104(3)which is wirelessly coupled to OFDM module 104(C) in device 102(D). Eachdevice 102(1)-(D) includes a transmitter, receiver, or transceiver toconvey output from one OFDM 104 module to another OFDM module 104. Thesetransmitters, receivers, or transceivers may be configured to convey theoutput via an electrical conductor, electromagnetic radiation, or both.Each device 102(1)-(D) includes one or more processors (not shown) and amemory (not shown) coupled to the processor. This processor may beconfigured to execute instructions stored in the memory.

Devices 102(1)-(D) may include wireless access points, radio frequencytransceivers, software defined radios, modems, interface cards, cellulartelephones, portable media players, desktop computers, laptops, tabletcomputers, netbooks, personal digital assistants, servers, standalonetransceiver interfaces, and so forth.

A tone selection module 110 may be present within device 102(4). Toneselection module 110 generates and may output one or more OFDM toneconfigurations 112. These tone configurations 112 meet one or morepre-determined constraints. In one implementation, constraints mayinclude ability to re-use an existing interleaver/deinterleaver,specific modulation such as 256-QAM, and so forth. The process utilizedby the tone selection module 110 is discussed in more detail below withregards to FIGS. 2 and 3.

Tone configuration 112 may then be implemented within OFDM modules104(1)-(C) for use in transferring information between two or moredevices 102(1)-(D). As described above, the tones in the toneconfiguration 112 may be selected to facilitate re-use of existingcomponents such as the interleaver/deinterleaver.

FIG. 2 is a flow chart for an example process 200 for selecting toneswith a tone selection module 110. Selected tones may be used by an OFDMmodule 104. The order in which the method is described is not intendedto be construed as a limitation, and any number of the described methodblocks can be combined in any order to implement the method, oralternate method. Additionally, individual blocks can be deleted fromthe method without departing from the spirit and scope of the subjectmatter described herein. Furthermore, the method can be implemented inany suitable hardware, software, firmware, or a combination thereof,without departing from the scope of the invention.

At block 202, the tone selection module 110 accepts a selection of anumber of data subcarriers N_(SD) to test. N_(SD) may be selected tomaintain compatibility with an existing OFDM system. For example, anOFDM system with a 40 MHz channel bandwidth may be modified to 80 MHzchannel bandwidth to increase data capacity. For the following examples,assume at least 1 tone is assigned to DC, at least 7 tones will beutilized for guard, and the 40 MHz system uses 108 data tones. Doublingthe channel bandwidth from 40 MHz to 80 MHz would double the number ofdata tones, thus N_(SD)=2*108=216 data tones.

At block 204, a number of coded bits per symbol N_(CBPS)=N_(SD)*M iscomputed where M comprises a modulation order. This modulation order maybe used to represent characteristics of the subcarrier modulation. Inone implementation, the modulation order may comprise one of thefollowing integer values:

1 for a binary phase-shift keying (BPSK) modulation;

2 for a quadrature phase-shift keying (QPSK) modulation;

4 for quadrature amplitude modulation (QAM) with 16 states (16-QAM);

6 for QAM with 64 states (64-QAM);

8 for QAM with 256 states (256-QAM); or

10 for QAM with 1024 states (1024-QAM).

Continuing the example above, assume BPSK will be assessed initially.Thus, N_(CBPS)=N_(SD)*M=216*1=216 coded bits per symbol. At block 206, anumber of coded bits per single carrier N_(BPSCS)=N_(CBPS)/N_(SD) iscalculated. Continuing the example from above, N_(BPSCS)=216/216=1. Atblock 208, N_(ROW)=y*N_(BPSCS) is computed, where y is an assignedinterleaver parameter. Thus, the number of rows in an OFDM interleaverare y*N_(BPSCS). As shown below with regards to table 20-16, in someOFDM systems where y=4, N_(ROW)=4*N_(BPSCS), while in other systemswhere y=6, N_(ROW)=6*N_(BPSCS), and so forth. Given a specified N_(ROW)and N_(BPSCS), y may be determined.

In an OFDM module 104, an interleaver intersperses constituents of twoor more codewords together before transmission on a channel. Adeinterleaver reverses this process. In some implementations a modifiedversion of an interleaver used in Institute of Electrical andElectronics Engineers (IEEE) 802.1-compliant OFDM systems may be used.This channel interleaver is defined in section 20.3.11.7.3 of the IEEEP802.11n/D6.0, “Draft Standard for InformationTechnology-Telecommunications and information exchange betweensystems—Local and metropolitan area networks—Part 11: Wireless LANMedium Access Control (MAC) and Physical Layer (PHY) specifications.”From this text, interleaver parameters from Table 20-16 “Number of Rowsand columns in the interleaver” are shown below.

TABLE 20-16 Bandwidth 20 MHz 40 MHz N_(COL) 13 18 N_(ROW) 4* N_(BPSCS)6* N_(BPSCS) N_(ROT) 11 29

These parameters define the number of coded symbols stored in theinterleaver. Continuing the example above for expanding from a 40 MHzchannel bandwidth to 80 MHz channel bandwidth, the existing interleaverand associated algorithms may be reused. Such reuse calls formodification of the interleaver to accommodate a matrix defined to writeand read data in the OFDM system with the greater channel bandwidth.These parameters include N_(ROW) and N_(COL) which define the number ofcoded symbols stored in the interleaver. Thus, continuing the example,N_(ROW)=9*1=9. In accommodating the larger matrix, N_(ROT) is used todefine a rotation of values when more than one spatial stream exists.N_(ROT) may be ignored because it does not define the interleaver sizeand thus does not affect tone selection.

At block 210, INT_(DIM)=N_(ROW)*N_(COL) is computed. In this example,assuming N_(COL)=24 (as shown below with regards to FIG. 4) thenINT_(DIM)=9*24=216. At block 212,

$Z = \frac{N_{CBPS}}{{INT}_{DIM}}$

is computed. In this example, Z=216/216=1.

At block 214, M₁=Z−[Z] is computed. Continuing the example, Z=1−1=0. Atblock 216, a number of data bits per symbol N_(DBPS)=r*N_(CBPS), where ris a code rate, is computed. Code rate indicates the portion ofnon-redundant information present when data is encoded. For thisexample, assume a code rate of ½, indicating that half of the dataactually transmitted is non-redundant, while the other half is redundantsuch as may be included due to error correction protocols. Thus,N_(DBPS)=½*216=153. At block 218, M₂=N_(DBPS)−└N_(DBPS)┘. In thisexample, M₂=153−└153┘=0.

Certain tone selections may fail to work properly with certainmodulation techniques. Thus, it may be useful to test configurations toconfirm a particular combination of code rate and modulation is valid. Aparticular combination may be considered valid when that combinationwill function using an existing or minimally extended OFDM component,such as an interleaver. In other words, will a particular combination ofcode rate and modulation work with a given tone selection? For example,in some OFDM systems, non-integer numbers of bits cannot be processeddue to the mapping done in encoding, modulation. It is possible withcertain selections of coding, modulation and tone selection that thetest at block 214 passes, but the result is a non-integer number forN_(DBPS) results. An information bit must be a full bit, as OFDM cannotencode information in a partial bit. In some implementations, bitpadding may be used to take non-integer numbers of bits and addadditional bits to produce an output with an integer number of bits.

When bit padding is not in use, the constraints as shown within thedotted line at 220 may be used to limit output of tone selections tothose which have integer numbers of bits. This may also limit code rateswhich are available. For example, using 256-QAM, code rates of ⅔ and ⅚may not be available without extensive modification to existing OFDMsystems. Such modification may render the resulting OFDM systemincompatible with prior OFDM systems.

At block 222, a test is performed to determine if M₁=0. When this testis true, block 224 tests to determine if M₂=0. As mentioned above, insome implementations where bit padding is available, or theseconstraints shown within 220 otherwise do not apply, they may beomitted. Continuing the above example, M₁=0 and M₂=0, therefore theconfiguration is valid. When block 222 or 224 result in a false output,the process may continue to block 228 below to determine if all tonecounts have been tested.

At block 226, a resulting tone selection may be saved as a validconfiguration. The previous acts may be looped until all available tonecounts are tested. At block 228, when all tone counts have been tested,the process then proceeds to block 230 and the search concludes. Resultsfrom this process may then be stored to computer-readable storage media,presented to a user, and so forth.

When block 228 determines tone counts remain to be tested, at block 232N_(SD)=N_(SD)−1 is computed. The results may be returned to block 204for the process to continue until all tone counts have been tested.

FIG. 3 is an example script for selecting tones for use by the OFDMmodule 104. This script is written for use with the MATLAB simulationtool for one implementation of a tone count selection module 110. MATLABis a product of The MathWorks Inc. of Natick, Mass. This script isprovided as an example, not as a limitation.

Within this script, the process iterates over a set of possible datatones in the range of 216 to 248. The 216 value was chosen as describedabove. Legacy OFDM systems used a total of 64 tones in conjunction witha 20 MHz channel bandwidth, and 128 tones in conjunction with a 40 MHzchannel bandwidth. In order to reuse the same tone spacing of the legacysystems and thus maximize reuse of hardware and software, an 80 MHzchannel bandwidth system would use 256 tones. Given this constraint of256 tones, 248 is chosen because with 256 tones total, only 8 toneswould be available for other uses including pilot, guard, and DC. Giventhat 8 tones may be impractically limiting for an OFDM system, 248 wasselected in this example as an upper bound.

Next, an inner loop iterates over the N_(COL) interleaver dimension. Inthis example, this loop iterates from 1 to 12, which maps a column sizeof 18 to 30 in an interleaver. In a wireless protocol defined byspecification IEEE 802.11, the column size was 13 for 20 MHz bandwidthand 18 for 40 MHz bandwidth, thus a range of 18 to 30 is appropriate foran OFDM system having an 80 MHz bandwidth.

The next inner loop is for the N_(ROW) count, which is allowed to runfrom 6 to 12 in this example. In the wireless protocol defined byspecification IEEE 802.11, the row multiplier is 4 for 20 MHz, 6 for 40MHz, thus a range of 6 to 12 is appropriate for 80 MHz. The next twoinner loops are for the modulation and code rate. The code rate may beselected based on the modulation type.

FIG. 4 is a table of illustrative possible configurations 400 generatedusing the script of FIG. 3 for an OFDM system having an 80 MHzbandwidth. In some implementations, these tone configurations 112 may beapplied to a wireless networking protocol using OFDM, including but notlimited to those related to the IEEE 802.11 standard. In generating thistable of configurations 400 the following assumptions were made of an 80MHz bandwidth OFDM system having tone spacing, modulation, and codingrates present in existing systems. These constraints are included tomaximize reuse of software and hardware designs, and may also provide anavenue for backward compatibility.

Based on this configuration and assuming no changes in the 80 MHz systemfor coding or modulation, several configurations shown at 400 arepossible. In one implementation, the same tone assignment for the guardtones, pilot tones, and DC as in a 40 MHz system may be used. Forexample, in the 40 MHz system there are 11 guard, 6 pilot, and 3 DCtones, for a total of 20 tones. Therefore, data tone assignments largerthan 256−20=236 are not available.

In another implementation, a 234 data tone configuration may besuitable. This configuration allows an additional 2 tones to beallocated to pilot, guard, or other use. In another implementation, 232tones may be allocated, which would provide 4 additional tones for pilotor guard functions.

FIG. 5 is a table 500 of possible tone configurations based on a portionof the possible configurations of FIG. 3. In a wireless networkingsystem, additional code rates and modulation types may be included toincrease peak data rates. In the table 500, a 256 state QAM modulationand a 1024 state QAM as well as a code rate of r=⅞ have been introduced.

Given the 256-QAM and 1024-QAM and a code rate r=⅞, the process of FIG.2 as implemented by the script of FIG. 3 may be used to determinepossible tone configurations 112. The configurations of the table 500are focused on tone counts under the 236 tone count arrived above, andabove a tone count of 230. When N_(SD)=234 all code rates ¾, ⅚, and ⅞are available, providing flexibility in selection. In comparison, whenN_(SD)=232 only the ¾ and ⅞ code rates are supported.

CONCLUSION

Although specific details of illustrative methods are described withregard to the figures and other flow diagrams presented herein, itshould be understood that certain acts shown in the figures need not beperformed in the order described, and may be modified, and/or may beomitted entirely, depending on the circumstances. As described in thisapplication, modules and engines may be implemented using software,hardware, firmware, or a combination of these. Moreover, the acts andmethods described may be implemented by a computer, processor or othercomputing device based on instructions stored on memory, the memorycomprising one or more computer-readable storage media (CRSM).

The CRSM may be any available physical media accessible by a computingdevice to implement the instructions stored thereon. CRSM may include,but is not limited to, random access memory (RAM), read-only memory(ROM), electrically erasable programmable read-only memory (EEPROM),flash memory or other solid-state memory technology, compact diskread-only memory (CD-ROM), digital versatile disks (DVD) or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium which can be used to store the desiredinformation and which can be accessed by a computing device.

1-20. (canceled)
 21. A method performed by a communication deviceconfigured to operate over different channel bandwidths, the methodcomprising: determining whether bit padding is available; in response todetermining that bit padding is unavailable, iterating through aplurality of total data tone counts to determine particular tone datacounts that satisfy:${{\frac{N_{CBPS}}{{INT}_{DIM}} - \left\lfloor \frac{N_{CBPS}}{{INT}_{DIM}} \right\rfloor} = 0},{{N_{DBPS} - \left\lfloor N_{DBPS} \right\rfloor} = 0},$ and where N_(CBPS) is a number of coded bits per symbol, INT_(DIM) is anumber of coded symbols stored in an interleaver, and N_(DBPS) is anumber of data bits per symbol; and selecting a total data tone count,from among the particular tone data counts, for modulating a datapayload in accordance with orthogonal frequency division multiplexing(OFDM) transmission in an OFDM system over an identified one of thechannel bandwidths.
 22. The method of claim 21, further comprising:interleaving two or more codewords in the data payload beforetransmission on a channel of the identified channel bandwidth using theinterleaver, wherein the number of coded symbols stored in theinterleaver is proportional to an assigned interleaver parameter times anumber of coded bits per single carrier.
 23. The method of claim 21,further comprising: determining whether iteration through the pluralityof total data tone counts has been completed, and in response todetermining that iteration through the plurality of total data tonecounts has been completed, presenting the particular tone data counts ona display.
 24. The method of claim 21, further comprising: aftercompleting iteration through the plurality of total data tone counts anddetermining that no particular tone data counts were determined,presenting on a display the plurality of total data tone counts and anindication that no particular tone data counts were determined.
 25. Themethod of claim 21, further comprising: in response to determining thatbit padding is available, selecting the total data tone from among theplurality of total data tone counts free from iterating through theplurality of total data tone counts to determine the particular tonedata counts.
 26. The method of claim 21, further comprising: determiningwhether a set of the particular tone data counts result in a non-integernumber of data bits per symbol; determining that non-integer numbers ofbits are unable to be processed in the OFDM system; and limitingselection of the total data tone count to avoid selection of the set ofthe particular tone data counts in response to determining thatnon-integer numbers of bits are unable to be processed and that bitpadding is unavailable.
 27. The method of claim 21, wherein: the numberof coded bits per symbol is equal to a number of data subcarriers timesa modulation order, and the number of data bits per symbol is a coderate times the number of coded bits per symbol.
 28. The method of claim27, further comprising: determining whether a set of the particular tonedata counts result in a non-integer number of data bits per symbol;determining that non-integer numbers of bits are unable to be processedin the OFDM system; and limiting selection of code rates in response todetermining that non-integer numbers of bits are unable to be processedand that bit padding is unavailable.
 29. The method of claim 21, furthercomprising: reusing the interleaver when expanding from a smallerchannel bandwidth to a larger channel bandwidth by modifying theinterleaver to accommodate a matrix defined to write and read data inthe OFDM system with the greater channel bandwidth.
 30. The method ofclaim 29, wherein: parameters of the matrix comprise N_(ROW) andN_(COL), which define a number of coded symbols stored in theinterleaver, and N_(ROT), which defines a rotation of values when morethan one spatial stream exists, a size of the interleaver is independentof N_(ROT), and N_(ROT) is ignored when selecting the total data tonecount.
 31. An apparatus of a communication device, the apparatuscomprising: processing circuitry configured to: iterate, whenpredetermined conditions are met, through a plurality of total data tonecounts to determine particular tone data counts that satisfy:${{\frac{N_{CBPS}}{{INT}_{DIM}} - \left\lfloor \frac{N_{CBPS}}{{INT}_{DIM}} \right\rfloor} = 0},{{N_{DBPS} - \left\lfloor N_{DBPS} \right\rfloor} = 0},$ and where N_(CBPS) is a number of coded bits per symbol, INT_(DIM) is anumber of coded symbols stored in an interleaver, and N_(DBPS) is anumber of data bits per symbol; select a total data tone count, fromamong the particular tone data counts; and modulate a data payload inaccordance with orthogonal frequency division multiplexing (OFDM)transmission in an OFDM system over an identified one of the channelbandwidths based on the total data tone count; and a transceiverconfigured to communicate using the identified one of the channelbandwidths.
 32. The apparatus of claim 31, further comprising: aninterleaver configured to interleave two or more codewords in the datapayload before transmission on a channel of the identified channelbandwidth, wherein the number of coded symbols stored in the interleaveris proportional to an assigned interleaver parameter times a number ofcoded bits per single carrier.
 33. The apparatus of claim 31, wherein:the processing circuitry is further configured to determine whetheriteration through the plurality of total data tone counts has beencompleted, and the apparatus further comprises display circuitryconfigured to, after iteration through the plurality of total data tonecounts has been completed, present one of: the particular tone datacounts, or after the processing circuitry has determined that noparticular tone data counts were determined, the plurality of total datatone counts and an indication that no particular tone data counts weredetermined.
 34. The apparatus of claim 31, wherein the processingcircuitry is further configured to: in response to a determination thatbit padding is available, select the total data tone from among theplurality of total data tone counts free from iterating through theplurality of total data tone counts to determine the particular tonedata counts.
 35. The apparatus of claim 31, wherein the processingcircuitry is further configured to: determine whether a set of theparticular tone data counts result in a non-integer number of data bitsper symbol; determine that non-integer numbers of bits are unable to beprocessed in the OFDM system; and limit selection of the total data tonecount to avoid selection of the set of the particular tone data countsin response to determining that non-integer numbers of bits are unableto be processed and that bit padding is unavailable.
 36. The apparatusof claim 31, wherein: the number of coded bits per symbol is equal to anumber of data subcarriers times a modulation order, and the number ofdata bits per symbol is a code rate times the number of coded bits persymbol, and the processing circuitry is further configured to: determinewhether a set of the particular tone data counts result in a non-integernumber of data bits per symbol; determine that non-integer numbers ofbits are unable to be processed in the OFDM system; and limit selectionof code rates in response to determining that non-integer numbers ofbits are unable to be processed and that bit padding is unavailable. 37.A non-transitory computer-readable storage medium that storesinstructions for execution by one or more processors of a communicationdevice to configure the communication device for multiple bandwidthoperation, the instructions to configure the communication device to:iterate, when predetermined conditions are met, through a plurality oftotal data tone counts to determine particular tone data counts thatsatisfy:${{\frac{N_{CBPS}}{{INT}_{DIM}} - \left\lfloor \frac{N_{CBPS}}{{INT}_{DIM}} \right\rfloor} = 0},{{N_{DBPS} - \left\lfloor N_{DBPS} \right\rfloor} = 0},$ and where N_(CBPS) is a number of coded bits per symbol, INT_(DIM) is anumber of coded symbols stored in an interleaver, and N_(DBPS) is anumber of data bits per symbol; select a total data tone count, fromamong the particular tone data counts; modulate a data payload inaccordance with orthogonal frequency division multiplexing (OFDM)transmission in an OFDM system over an identified one of the channelbandwidths based on the total data tone count; interleave a plurality ofcodewords in the data payload before transmission on a channel of theidentified channel bandwidth using an interleaver, the number of codedsymbols stored in the interleaver proportional to an assignedinterleaver parameter times a number of coded bits per single carrier,the interleaver being reused when expanding from a smaller channelbandwidth to a larger channel bandwidth by modification of theinterleaver to accommodate a matrix defined to write and read data inthe OFDM system with the greater channel bandwidth; and communicateusing the identified one of the channel bandwidths.
 38. The apparatus ofclaim 37, wherein the instructions further configure the communicationdevice to: determine whether iteration through the plurality of totaldata tone counts has been completed, and after iteration through theplurality of total data tone counts has been completed, present one of:the particular tone data counts, or after the processing circuitry hasdetermined that no particular tone data counts were determined, theplurality of total data tone counts and an indication that no particulartone data counts were determined.
 39. The apparatus of claim 37, whereinthe instructions further configure the communication device to: inresponse to a determination that bit padding is available, select thetotal data tone from among the plurality of total data tone counts freefrom iterating through the plurality of total data tone counts todetermine the particular tone data counts.
 40. The apparatus of claim37, wherein the instructions further configure the communication deviceto: determine whether a set of the particular tone data counts result ina non-integer number of data bits per symbol; and one of: determine thatnon-integer numbers of bits are unable to be processed in the OFDMsystem; and limit selection of the total data tone count to avoidselection of the set of the particular tone data counts in response todetermining that non-integer numbers of bits are unable to be processedand that bit padding is unavailable, or determine that non-integernumbers of bits are unable to be processed in the OFDM system, and limitselection of code rates in response to determining that non-integernumbers of bits are unable to be processed and that bit padding isunavailable.